(1) Field of the Invention
The present invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of monitoring tool performance using a multivariate advanced process control system in the fabrication of integrated circuit devices.
(2) Description of the Prior Art
Run by Run (RBR) feedback control schemes have been used widely to control and monitor the semiconductor manufacturing processes. Statistical process control is combined with feedback control and uses data from past runs to adjust the recipe for the next run. This method offers the potential for reducing process variability caused by equipment aging, chemical depletion, or fluctuation in ambient conditions with a minimal cost. Most literature in the RBR control, however, is only applicable to the manufacturing process with a single product by a single tool. For a foundry industry, due to different customer requirements, one of the most popular production styles is multiple products by multiple tools. For example, if a process runs eight products by five tools, then there are forty combinations which will lead to a very complex situation using conventional RBR control schemes. If separate feedback schemes are set up for each combination, besides affecting the efficiency of the RBR control schemes, this method also ignores the useful information between the tools and products. For example, under a specific tool, an individual control scheme does feedback only on a specific product and it loses the opportunity to adjust for other products produced by the same tool. In addition, since customer orders may not be continuous and scheduled tool set-up may change from time to time, the feedback scheme for any production lot cannot be successfully applied to the next production lot. Therefore, it is desired to provide a multiple run by run control process.
A number of patents address process control issues. For example, U.S. Pat. No. 5,943,550 to Fulford, Jr. et al teaches a method of controlling transistor drive current across a wafer by varying light exposure based on parameters such as gate oxide thickness, RTA temperature, polyetch bias, etc. U.S. Pat. No. 6,148,239 to Funk et al shows a process control system using feed forward control to label materials in groups having common properties based on process variables, tool variables, and material variables. U.S. Pat. No. 6,248,602 to Bode et al discloses a method to store control input parameters such as for overlay control in a photolithography process, process a lot of devices, collect and analyze data for the lot, and perform automated rework based on the data analysis. U.S. Pat. No. 6,245,581 to Bonser et al teaches a method of measuring critical dimension, analyzing the measurement, and performing a secondary etch process based on the analysis.